The invention relates in general to methods of treating contaminated sediments, and in particular to the treatment of metal-contaminated sediments.
Significant numbers of sediments in deepwater, wetland, and dry land environments are contaminated with various metals. For example, metals which are introduced by one means or another into lakes, marshes, river beds and ocean areas near coastlines, settle on the bottoms of such bodies of water and become attached to sediments. The metal-contaminated sediments are detrimental to the ecosystem, especially wildlife which utilizes the body of water, such as fish, foraging waterfowl and small vertebrates and invertebrates.
One method of treating metal-contaminated marine sediments in situ is disclosed in “Contaminated Sediments in Ports and Waterways, Cleanup Stragegies and Technologies”, Marine Board, National Research Council, pages 97–99 (1997). Sulfides or elemental sulfur are used to promote the formation of metal sulfides, which have low solubility in water and therefore tend to form precipitates.
“Regional Geochemistry of Metals in Organic-Rich Sediments, Sawgrass and Surface Water, from Taylor Slough, Fla.”, U.S. Department of the Interior, USGS, OFR-00-327, pages 1–5 (2002), discloses that sulfur plays an important role in the sequestration of metals in sedimentary systems. Under anoxic (chemically reduced) conditions, microbial sulfate reduction reduces sulfate to sulfide. It is described that sulfide is a highly reactive chemical species, especially with metal ions, and will quickly form highly insoluble metal sulfides.
“Immobilization of Cobalt by Sulfate-Reducing Bacteria in Subsurface Sediments”, Krumholz et al., published in Geomicrobiology Journal, Volume 20, No. 1/Jan–Feb, 2003, pages 61–72, discloses that an increase in the amount of cobalt (Co2+) immobilized as CoS was observed as sulfate reduction activity was stimulated in flow-through columns.
Although the current treatment methods are somewhat effective, there is still a need for an improved method of treating metal-contaminated sediments.